Choice "C" is correct. This answer choice contains both demand-pull inflation (when the aggregate demand curve shifts right) and cost-push inflation (when the short-run aggregate supply curve shifts left). An increase in aggregate demand causes output to rise and the price level to rise. A decrease in aggregate supply causes output to fall and the price level to rise. Thus, an increase in aggregate demand and a decrease in aggregate supply is the most inflationary.Choice "a" is incorrect. If aggregate supply increases, the price level will fall (reducing inflation).
Choice "d" is incorrect. If aggregate demand decreases, the price level will fall (reducing inflation).
Choice "b" is incorrect per above explanation.